Stable oxide encapsulated metal clusters and nanoparticles

Abstract

The present invention discloses stable, non-agglomerated, ultra-small metal/alloy clusters encapsulated in silica with the metal/alloy cluster size of less than 5 nm. The invention further discloses a simple, cost effective process for the preparation of metal/alloy clusters encapsulated in silica which is thermally stable and without agglomeration.

We claim: 
     
       1. A process for synthesis of stable, non-agglomerated ultra-small clusters of metals/alloy having size less than 5 nm encapsulated in mono-disperse silica particles comprising;
 a. obtaining metal/alloy-thiolate clusters of less than 2 nm by modified Brust method using a 3:1 ratio of metal/alloy:thiol in a 1:1 mixture of methanol and water, using thiolate ligand N, N, N-Tripropyl (11-mercaptoundecyl) ammonium Chloride; 
 b. encapsulating with silica by a one step hydrolysis using tetraethyl orthosilicate (TEOS) in ethanol-water mixture to obtain monodisperse silica spheres encapsulating the metal/alloy clusters having a size less than 2 nm, and 
 c. further comprising calcining the monodisperse silica particles encapsulating the ultra-small metal/alloy clusters under a flow of air at 350° C., to obtain stable metal/alloy clusters with a nanoparticle size of less than 5 nm. 
 
     
     
       2. The process for the encapsulation according to  claim 1 , wherein the ultra-small clusters of metal/alloy are encapsulated in mono disperse silica particles of 20-30 nm diameter.